Super engineering plastics have been used in a wide range of applications in such fields as electric⋅electronic engineering, aircraft and space engineering, automotive industries, medicines and in industries in general. Among the super engineering plastics, in particular, an polyaryletherketone has been expected because of its excellent chemical and physical properties. The super engineering plastics featuring a variety of advantages, however, are also accompanied by such problems that they bend easily and are easily worn out. To improve these problems, there has been generally known a method of obtaining the resin as a composite material by adding a filler thereto.
Here, the restorative work in the dental treatment has heretofore been carried out by either filling a dental composite resin or by using a prosthetic material such as inlay, crown or bridge.
The latter method consists of the steps of forming a cavity or forming an abutment tooth, forming impression, forming a gypsum model and preparing a prosthetic, and, thereafter, adhering and joining the prosthetic to the cavity or the abutment tooth. When the prosthetics are made of a metal as represented by a gold-silver-palladium alloy, there is representatively employed a complex mold casting method called lost wax casting.
As described above, preparation of prosthetics has, so far, required a complex and minute work necessitating skillful dental technicians and a lot of working time, i.e., necessitating a tremendous amount of time and cost. Moreover, use of the above alloy is accompanied by such problems as metal allergy, depletion of resources, fluctuation in price and so on.
On the other hand, recent development in the CAD/CAM systems is now making it possible to prepare precise dental prosthetics in short periods of time and in large quantities relying on the milling work by utilizing the above systems. There have now been placed in the market CAD/CAM systems for designing and preparing the prosthetics.
The milling work based on the CAD/CAM system can deal with the works or blocks of such shapes as rectangular parallelepiped, cylinder, disc, etc. As the material for constituting the blocks, ceramics were, first, considered accompanied, however, by the problems in regard to the workability due to their high hardness, damage to the natural teeth after the prosthetic has been fitted and high prices. In recent years, therefore, study has been forwarded to develop blocks comprising inorganic filler materials and resins.
In the resin materials for blocks developed thus far, however, the resin components that served as base materials were all thermosetting acrylic resins (cured polymers of acrylic monomers) (patent documents 1, 2 and 3). Therefore, the resin materials were poor in their mechanical strength and were not strong enough for use as prosthetics for true molar teeth or bridges on where high pressures of occlusion were subject to be applied.
On the other hand, attempts have been made to use a super engineering plastic as a dental material that needs a large mechanical strength. However, nothing has yet been disclosed concerning the problems that might occur during the milling work of the above material. In particular, nothing has been brought into attention concerning the occurrence of voids when the dental material is melt-formed or concerning the effects of voids upon the appearance of the formed body, defects in the formed body, mechanical strength or workability of milling (patent document 4).